Teaching one’s son verses of Torah:
Although a child is exempt from all the Mitzvos, and even the father is not Biblically obligated to educate him in Mitzvos, but rather only Rabbinically, nevertheless, teaching Torah is a Biblical positive command. The father is commanded to teach his small son Torah, even though the son himself is not obligated [to learn Torah or keep Mitzvos, and has not yet even reached the age of Chinuch].
From what age? From what age is a father obligated to teach his son Torah? As soon as one’s son begins to speak, his father is Biblically obligated to teach him Torah. At the very beginning, when he first begins to talk, he is to teach him the verse of “Torah Tziva Lanu Moshe” and the first verse from the Parsha of “Shema Yisrael.” [Teaching these verses root into the young child belief in Hashem and love of the Torah.] Afterwards, he is to teach him other verses, one verse at a time, so that the child knows them by heart.
 Admur Hilchos Talmud Torah 1/1; Michaber 245/1; Rambam 1/5; Kiddushin 29a
 See Piskei Dinim Tzemach Tzedek 350
 The reason: As the verse states “Ulimadetem Osam Es Bneichem Lidaber Bam.” [ibid]
 Admur Hilchos Talmud Torah 1/1; Michaber 245/5; Rambam Talmud Torah 1/6; Sifri Eikev 11; Sukkah 42a
 This is approximately at two years old. [Likkutei Sichos 21/343 footnote 40 based on Radak] Others say it is when the child knows how to speak fluently, which is approximately at age 4. [Aruch Hashulchan 245/2]
 Igros Kodesh Rashab 2/483